This invention relates to a staring or static type horizon sensor using linear arrays of infrared detectors having the horizon to be detected imaged thereon in which the elements of the array are interconnected in groups of repetitive patterns of alternating polarity whose outputs are processed to provide attitude information.
The two main categories of horizon sensors are scanning and staring or static types. The scanning sensor mechanically scans the image of the earth over an infrared detector whose signal output is used to determine the attitude of the horizon sensor with respect to the earth. These sensors provide good accuracy over a wide angular range but have limited reliability due to moving parts.
In the staring or static type horizon sensor, the horizon is imaged onto an infrared detector so that the edge of the earth's image falls in the infrared detector's active area which senses the thermal discontinuity between the relatively warm earth and cold space and uses this information to determine the attitude of the spacecraft on which the sensor is positioned. Since the earth's radiance is non-uniform and unpredictable even in the most favorable optical band due to latitude, season and the weather, the staring sensor causes errors that increase with the angular extent of the earth subtended by the sensor's field-of-view. By dividing the field-of-view into many small sized elements, a simple linear array of infrared detectors offers extended range and higher accuracy than the staring sensor having larger areas and fewer elements. The disadvantage of the multidetector linear arrays is the requirement of sampling and processing the signal outputs of each element in the array which requires a multiplicity of electronic switches and processing electronics to convert the output signals to usable information.